1. Field of the Invention
The invention relates to a plasma-enhanced chemical vapor deposition (PECVD) apparatus to be used for forming a thin film in a process of fabricating a semiconductor device, and more particularly to a plasma-enhanced chemical vapor deposition apparatus capable of uniformly forming a metal film having a high barrier characteristic.
2. Description of the Related Art
In these days, a design-rule in a semiconductor device is leveled up from a half-micron level to a quarter-micron level as LSI has been fabricated in a smaller size and in higher integration. In addition, techniques of forming a multi-layered wiring structure and planarizing a surface of a device makes an aspect ratio of a contact hole for connecting upper and lower wiring layers with each other higher and higher. In order to form a highly reliable multi-layered wiring structure including such a contact hole having a high aspect ratio, various methods have been used. For instance, one of such methods includes the steps of forming a titanium nitride layer acting as a barrier metal, conformal to a wiring layer for preventing diffusion of material of which the wiring layer is composed, forming an aluminum film, and thermally treating the aluminum film into fluid to thereby flow the fluidized aluminum into a contact hole. Another method includes the step of filling a contact hole with material of which an upper wiring layer is composed or a contact plug by selective chemical vapor deposition or blanket chemical vapor deposition of tungsten.
A titanium layer and a titanium nitride layer are formed generally by sputtering or reactive sputtering wherein titanium is used as a target material. Improvement has been made in these methods in order to fulfill a demand of forming a contact hole having a higher aspect ratio. That is, there have been suggested improvements in sputtering such as collimated sputtering wherein a vertical component of movement of particles obtained by sputtering is enhanced, and long throw sputtering wherein a vertical component of movement of particles obtained by sputtering by spacing a target from a substrate.
However, as an aspect ratio of a contact hole becomes higher and higher, it is difficult to form a thin film sufficiently at a bottom of a contact hole even in accordance with any one of the above-mentioned methods. In addition, in accordance with any one of the above-mentioned methods, a film is deposited at an opening of a contact hole in an over-hang shape, which exerts a harmful influence on a subsequent step of forming a wiring layer, and reduces reliability of a wiring layer formed on such a contact hole. Furthermore, any one of the above-mentioned sputtering provides a quite low film deposition rate, which reduces productivity of a thin film to be formed on a semiconductor substrate.
In order to solve the above-mentioned step coverage in sputtering, there has been suggested a plasma-enhanced chemical vapor deposition wherein a thin film is grown on a semiconductor substrate with the semiconductor substrate being heated, for instance, by J. T. Hillman et al., xe2x80x9cTitanium Chemical Vapor Depositionxe2x80x9d, VLSI Multilevel Interconnection Conference, pp. 365-367, 1994. In the suggested plasma-enhanced chemical vapor deposition, a titanium tetrachloride gas is employed as a process gas, and a titanium layer is formed by hydrogen reduction in a parallel plate type plasma-enhanced chemical vapor deposition apparatus. A titanium nitride film is formed conformal to a semiconductor substrate through the use of reduced pressure chemical vapor deposition.
FIG. 1 illustrates a typical conventional apparatus for carrying out plasma-enhanced chemical vapor deposition. The illustrated apparatus includes a reaction chamber 11 having an inlet port 11a through which a process gas is introduced into the reaction chamber 11, and a pair of outlet ports 11b through which an exhausted gas is discharged, a susceptor 12 composed of metal for placing a semiconductor substrate 13 such as a silicon substrate thereon, an electrode 14 located in facing relation with the susceptor 12 and cooperating with the susceptor 12 to generate plasma 15 therebetween for forming a thin film on the semiconductor substrate 13 placed on the susceptor 12, and an AC voltage source 16 for providing AC voltage to the electrode 14 for generating the plasma 15 between the susceptor 12 and the electrode 14.
However, in the conventional plasma-enhanced chemical vapor deposition apparatus illustrated in FIG. 1, since there occurs an expansion in gas plasma-enhanced chemical vapor deposition. The illustrated apparatus includes a reaction distribution when the plasma 15 is generated, and a portion of the susceptor 12 which is not covered with the semiconductor substrate 13 is exposed to the plasma 15, it is quite difficult or impossible to control a temperature of the susceptor 12. As a result, portions of the susceptor 12 have different temperatures, which causes poor uniformity of a thin metal formed by plasma-enhanced chemical vapor deposition on the semiconductor substrate 13, and also causes portions of the thus formed thin film to have different electric characteristics.
Furthermore, since a titanium nitride film has a polycrystalline structure including columnar crystals, a titanium nitride film formed as a barrier metal by means of the conventional plasma-enhanced chemical vapor deposition apparatus illustrated in FIG. 1 would include a lot of crystal grains, and resultingly have a low barrier characteristic.
As another example, Japanese Unexamined Patent Publication No. 59-92520 has suggested a chemical vapor deposition apparatus including a cylindrical inner bell jar having an inner shape similar to an outer shape of an electrode situated in a reaction chamber. The bell jar is designed to be axially movable relative to the electrode.
As still another example, Japanese Unexamined Patent Publication No. 7-226378 has suggested a plasma-enhanced chemical vapor deposition apparatus including a bell jar composed of silicon nitride and located above a semiconductor substrate. A titanium/titanium nitride film is successively formed in the apparatus by employing a mixture gas of TiCl4 and H2 and a mixture gas of TiCl4, H2, and N2.
The chemical vapor deposition apparatuses suggested in the above-mentioned Publications are accompanied with the same problems as mentioned above. That is, portions of a susceptor have different temperatures, which causes poor uniformity of a thin metal, and also causes portions of the thin film to have different electric characteristics. Furthermore, a titanium nitride film formed by means of the suggested chemical vapor deposition apparatuses would include a lot of crystal grains, and resultingly have a low barrier characteristic.
It is an object of the present invention to provide a plasma-enhanced chemical vapor deposition apparatus capable of enhancing uniformity in a thin film formed on a semiconductor substrate, and of improving an electric characteristic of a thin film to be used as a barrier film.
It is also an object of the present invention to provide a method of carrying out plasma-enhanced chemical vapor deposition capable of doing the same.
In one aspect of the invention, there is provided a plasma-enhanced chemical vapor deposition apparatus including (a) a reaction chamber into which a process gas is introduced and from which an exhausted gas is discharged, (b) a susceptor having a first region on which a semiconductor substrate is to be placed and a second region other than the first region, (c) an electrode located in facing relation with the susceptor and cooperating with the susceptor to generate plasma therebetween for forming a thin film on the semiconductor substrate placed on the first region of the susceptor, and (d) a ceramics insulator located between the second region of the susceptor and the plasma.
There is still further provided a plasma-enhanced chemical vapor deposition apparatus including (a) a reaction chamber into which a process gas is introduced and from which an exhausted gas is discharged, (b) a susceptor having a first region on which a semiconductor substrate is to be placed and a second region other than the first region, (c) an electrode located in facing relation with the susceptor and cooperating with the susceptor to generate plasma therebetween for forming a thin film on the semiconductor substrate placed on the first region of the susceptor, and (d) a ceramics insulator covering the second region of the susceptor therewith.
There is yet further provided a plasma-enhanced chemical vapor deposition apparatus including (a) a reaction chamber into which a process gas is introduced and from which an exhausted gas is discharged, (b) a susceptor having a first region on which a semiconductor substrate is to be placed and a second region other than the first region, (c) an electrode located in facing relation with the susceptor and cooperating with the susceptor to generate plasma therebetween for forming a thin film on the semiconductor substrate placed on the first region of the susceptor, (d) a susceptor cover composed of ceramics insulating material and covering the second region of the susceptor therewith, and (e) a partition member composed of ceramic insulating material for partitioning an inner wall of the reaction chamber and the plasma from each other.
It is preferable that the susceptor cover and the partition member are composed of the same material.
There is still yet further provided a plasma-enhanced chemical vapor deposition apparatus including (a) a reaction chamber into which a process gas is introduced and from which an exhausted gas is discharged, (b) a susceptor having a first region on which a semiconductor substrate is to be placed and a second region other than the first region, (c) an electrode located in facing relation with the susceptor and cooperating with the susceptor to generate plasma therebetween for forming a thin film on the semiconductor substrate placed on the first region of the susceptor, and (d) a susceptor cover composed of ceramics insulating material, and having a first portion covering the second region of the susceptor therewith and a second portion extending between an inner wall of the reaction chamber and the plasma for partitioning them from each other.
The second portion of the susceptor cover may be designed to further extend between an end of the electrode and the inner wall of the reaction chamber.
There is further provided a plasma-enhanced chemical vapor deposition apparatus including (a) a reaction chamber into which a process gas is introduced and from which an exhausted gas is discharged, (b) a susceptor having a first region on which a semiconductor substrate is to be placed and a second region other than the first region, (c) an electrode located in facing relation with the susceptor and cooperating with the susceptor to generate plasma therebetween for forming a thin film on the semiconductor substrate placed on the first region of the susceptor, and (d) a bell-jar shaped susceptor cover composed of ceramics insulating material, the bell-jar shaped susceptor cover having a bottom end open to the electrode and extending between an inner wall of the reaction chamber and the plasma for partitioning them from each other, and a top end covering the second region of the susceptor therewith and formed with an opening coextensive with the first region of the susceptor.
It is preferable that the bottom end of the bell-jar shaped susceptor cover further extends between an end of the electrode and the inner wall of the reaction chamber. It is preferable that the bell-jar shaped susceptor cover has a cross-section similar to a cross-section of the electrode.
It is preferable that the ceramics insulator or ceramics insulating material is composed of silicon nitride, or a-material containing oxygen therein such as quartz.
In another aspect of the invention, there is provided a method of carrying out plasma-enhanced chemical vapor deposition, including the steps of (a) introducing a process gas into a reaction chamber, (b) generating a plasma between a susceptor having a first region on which a semiconductor substrate is placed and a second region other than the first region, and an electrode located in facing relation with the susceptor so that the second region of the susceptor is partitioned from the plasma, and (c) discharging an exhausted gas out of the reaction chamber.
It is preferable that a thin film formed on the semiconductor substrate in the step (b) contains metal or metal alloy therein, preferably titanium or titanium nitride.
There is further provided a method of carrying out plasma-enhanced chemical vapor deposition, including the steps of (a) introducing a process gas into a reaction chamber, (b) generating a plasma between a susceptor having a first region on which a semiconductor substrate is placed and a second region other than the first region, and an electrode located in facing relation with the susceptor so that both the second region of the susceptor and an inner wall of the reaction chamber are partitioned from the plasma, and (c) discharging an exhausted gas out of the reaction chamber.
There is still further provided a method of carrying out plasma-enhanced chemical vapor deposition, including the steps of (a) introducing a process gas into a reaction chamber, (b) generating a plasma between a susceptor having a first region on which a semiconductor substrate is placed and a second region other than the first region, and an electrode located in facing relation with the susceptor so that both the second region of the susceptor and an inner wall of the reaction chamber are partitioned from the plasma and that an end of the electrode is partitioned from the inner wall of the reaction chamber, and (c) discharging an exhausted gas out of the reaction chamber.
In accordance with the present invention, a second portion of a susceptor is covered with a ceramics insulating material. Hence, it is possible to avoid the second portion of the susceptor from being directly exposed to plasma, which allows a temperature of the susceptor to be readily controlled. As a result, there is generated no dispersion in a temperature of the susceptor, namely, the susceptor has a common temperature in all portions thereof. Accordingly, a thin film formed on a semiconductor substrate has adequate uniformity, which ensures an enhanced device performance and an enhanced fabrication yield.
It would be possible to prevent diffusion of gas when plasma is generated, by employing an inner bell jar formed integrally with a susceptor cover, which further enhances a uniformity in a thin film formed on a semiconductor substrate.
When a titanium nitride film is to be formed on a semiconductor substrate, there is employed quartz as the ceramics insulating material. Since a titanium nitride film is grown slightly absorbing oxygen from the quartz, it is possible to prevent growth of grains, which ensures that crystal grains are significantly reduced. As a result, the formed titanium nitride film could have remarkably improved characteristics as a barrier film.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.